The rapid and effective repair of bone defects caused by injury, disease, wounds, or surgery is a goal of orthopedic surgery. Toward this end, a number of compositions and materials have been used or proposed for use in the repair of bone defects. The biological, physical, and mechanical properties of the compositions and materials are among the major factors influencing their suitability and performance in various orthopedic applications.
Autologous cancellous bone (“ACB”), also known as autograft or autogenous bone is considered the gold standard for bone grafts. ACB is osteoinductive and non-immunogenic, and, by definition, has all of the appropriate structural and functional characteristics appropriate for the particular recipient. Unfortunately, ACB is only available in a limited number of circumstances. Some individuals lack ACB of appropriate dimensions and quality for transplantation, and donor site pain and morbidity can pose serious problems for patients and their physicians.
Much effort has been invested in the identification or development of alternative bone graft materials. In the procurement and processing of xenograft or allograft, a prime consideration is minimizing the risk of transferring potentially harmful diseases to the bone recipient. In fact, provision of bone tissue safe for transplantation provides a very special challenge as immunogenic material and also microorganisms and viruses can be found deep within the internal matrix of bone samples.
Transplanting of contaminated bone can have serious consequences to the recipient. For example, transmission of human immunodeficiency virus (HIV) via bone grafting is well known. Accordingly, there is a great need for bone processing methods that decrease the risk of disease transmission associated with the use of, and preparation and procurement of, transplantable bone to the recipient. In this regard it is also important to recognize that even with a state of the art donor screening methodology, recent infections in a particular donor may not be detected, thereby underscoring the importance of improved cleaning and decontaminating treatments that offer prophylactic protection against potential, or as yet undetected, infectious agents.
Current methods for viral inactivation and sterilization involve the use of toxic chemicals, high temperature and/or irradiation. The harsh treatment of biological active materials such as bone grafting materials cause the degradation or decomposition of materials, destroy biological activity, for example osteoconductivity of demineralized bone tissue, and reduce mechanical properties significantly.
There are also significant limitations on the extent to which decontaminating agents have been used successfully to penetrate and to decontaminate the bone matrix. Bone tissue contains potentially removable materials, for example, marrow, cells and lipids that impede access of decontaminating agents deep into bone tissue where infectious agents or immunogenic macromolecules may be present.
Methods have been developed for treating bone tissue with carbon dioxide as part of critical point dehydration. Other methods have used supercritical carbon dioxide to achieve viral inactivation and/or terminal sterilization of bone tissue. Some of these methods required large amounts of carbon dioxide which have been costly. The carbon dioxide used in the treatment of bone tissue would also become contaminated with infectious agents and/or other solvents and, when released to the atmosphere, would have a negative environmental impact. Because in some instances the treatment of bone tissue was not automated, human error would contribute to an inefficient process that would provide an inconsistent product.
Accordingly, there is a need for automated, efficient methods of treating bone tissue without compromising the integrity of desirable biomaterials present in bone tissue and at the same time reduce costs associated with the use of large amounts of carbon dioxide, reduce or even eliminate human error, and provide product consistency while improving the environment.